A. Field of the Invention
This invention relates to electronic text editing and display systems and, more particularly, to a system in which the characters to be displayed are "closepacked" in a memory. A display controller calculates the memory addresses of the characters, retrieves the characters from memory and determines the endings of successive lines of displayed text.
B. Prior Art
Electronic text editing and display systems commonly include a digital data processor for editing the textual data to be displayed. In some systems, the processor is included in a single unit with an input device such as a keyboard and an output device such as a display at which the text being edited is reviewed; each input and display thus have associated with them a corresponding processor. However, such systems are quite expensive because a processor is included with each display. In other systems the processor operates with two or more display units. This reduces the costs of such systems, but introduces other complications.
Typically, in either system, the editing functions are performed primarily in, and controlled by, the processor. This places a substantial burden on the processor and, in cases where the processor is shared by more than one display, limits the number of display units the processor can service without unduly degrading the display.
One of the editing functions performed by text editing systems is margin control, that is, the accomodation of the displayed text to a preset margin so that words are not improperly split by running over the margin. Typically this is accomplished with the aid of the processor which monitors each line being displayed and terminates the line upon arriving at a word that is too long for display without runover. Line termination is accomplished by inserting a line-delimiting code into the text, which is stored in a memory. When the display controller retrieves the stored text, it responds to the line-delimiting code by causing the display to shift down to the next line. Thus, each time an editing function is performed which may move text from one line to another, the processor must recalculate line-delimiter positions for each successive line. In some cases this can result in the recalculation of most or all of these positions and, correspondingly, a substantial amount of repositioning of the line delimiting codes in the memory. A large amount of processor time may be needed for the operations, so the processor can therefore handle only a few editing stations.
Accordingly, it is an object of this invention to provide an improved text editing and display system.
Further, it is an object of the invention to provide an improved text editing and display system in which the central processor can be shared among a relatively large number of displays.
Another object of the invention is to provide an improved multi-display text editing system including a central processor in which the display burden on the central processor is greatly relieved.
Still another object of the invention is to provide apparatus for controlling the display of text in an electronic text editing and display system.